1. Field of Invention
The present invention relates to a compensation circuit. More particularly, the present invention relates to a slope compensation circuit for current-mode DC/DC converters.
2. Description of Related Art
In conventional current-mode controlled DC to DC (DC/DC) converters, there is usually a slope compensation circuit provided for changing the slope at which a reference signal intersects with a current sense signal. The slope compensation circuit is capable of outputting a slope compensation signal superimposed on the current sense signal, which is used as a control parameter, to avoid “open loop instability” or “sub-harmonic oscillation”.
In the past, the slope compensation signal was formed by transforming an oscillation signal from an oscillator and then superimposed on the current sense signal. However, the oscillation signal is referenced to a ground signal when being generated. Once the ground signal is unstable or has glitches, the slope compensation signal will be affected to have offsets and distortion. As a result, the “open loop instability” or “sub-harmonic oscillation” cannot be prevented efficiently, and even the DC/DC converters cannot work well.